Controlling the rate at which calls to one or more designated location(s) are allowed to enter a telecommunications network is often referred to as rate-based control. Such methods introduce call treatment which restrains the number of calls that can be sent from one or more switches (or all switches) in a network to designated locations during a period of time. It has long been a practice in administering telecommunications networks to provide call blocking methods under conditions of system or processor overload. For example, techniques are sometimes applied to call-in numbers for radio or TV call-in shows that experience a concentrated volume of calling in response to contest offers or celebrity appearances.
Other cases suitable for overload control countermeasures arise when fires, severe weather or other crisis conditions impose great demands on a communications network for calls originating and/or terminating at a particular switch or in a particular geographical region. The importance of throttling techniques is clear in modem processor-based switches and other network elements. If unchecked surges of demand persist for too long, the result can be a halt of operation of the processor and total shutdown.
In modem networks one typical approach in applying throttling techniques is to have traffic-sensitive controls imposed by messages sent from a network management control center or similar network facility to individual switches. Such a network management control center may include an administrative control station receiving traffic monitoring data, which data can be acted on by a control center operator. For example, a network management control center operator receiving information about unusual calling volumes to a particular number, group of numbers or switching location can cause a control instruction to be sent to selected switches, or all switches, in the network to block or otherwise inhibit additional traffic destined for the overloaded switch or group of switches.
As an example, call treatment imposed by network administration personnel in the face of unusually high calling volume to a particular switch may be applied to all switches in the network. The call treatment imposed on network switches may, for example, be such that originating volume directed to the high-volume switch (or a number or group of numbers at one or more switches) may be limited to a defined number of calls per unit time (e.g., seconds or minutes). While actions taken will vary, e.g., depending on the call treatment options available, the person or mechanism sending a control instruction may designate that blocked calls receive either an "all circuits busy" announcement, or a busy signal.
In addition to the manual imposition of call controls by call control messages sent from network management personnel to switches, it is well known in the art to use network databases, e.g., service control points or SCPs to automatically send such messages. In particular, these call treatment messages can be associated with messages sent in response to queries from a switch for database information, e.g., 8xx-to-POTS (Plain Old Telephone Service) number translation information. Such call treatment information and direction to be imposed by SCP messages in some cases is formed at a service management system (SMS) associated with one or more SCPs, and passed to the SCPs for use in responding to subsequent queries. Processor-based network nodes (e.g., switches) commonly interact with other nodes (e.g., other switches and SCPs), and provide useful output in response to one or more messages for each call. Typically, these messages are routed through a signaling network, such as signaling system 7 (SS7) networks in response to call requirements.
Processors appear in telecommunications networks in many applications; the cited voice call switching and SCP-based intelligent network 8xx voice calls are merely among the most common. Database processors appear in many modem telecommunications networks to provide a wide range of voice and data applications. ATM and other data packet- and cell-switches, routers, bridges and many other processor-based systems help provide voice-band and wideband applications.
Increasingly, telecommunications systems are called on to provide various levels of guaranteed service. Emergency calls, such as the ubiquitous 911 calls, have long been afforded priority treatment in the face of processor overload. Additionally, in many data networks, differing services are provided under respective quality of service (QoS) guarantees. Determining throttling strategies is more complex in the case of multiple call types because, inter alia, the quantity of required call processing resource may be different for each call type. Of course the mix of calls of each class that arrive at a processor that is in, or approaching, overload will typically vary with time as well.
When call treatment is to be imposed because of overload at a data switch processor, e.g., it becomes important to impose these call treatments in such manner as to avoid or minimize violations of agreed-upon level of service guarantees. Even without express QoS goals, an appropriate balance often must be maintained for calls of different types or classes. For example, in circuit switch networks where 800 and residential calls are supported, it is important that the total throughput from both calls is maximized. It is desirable to detect overload using indicators such as signaling message delay inside the system, and take actions such as traffic throttling based not only on indicator values, but also on call blocking criteria appropriate to various type calls supported by the system.
While many solutions have been attempted to avoid processor or system overload in the course of seeking to maximize useful throughput in a telecommunications system, success has been mixed. For networks handling only a single call type, overload control has usually been based on throttling traffic before it enters the communications processor. This throttling has taken many forms: for example, accepting calls only with a pre-determined probability or only within certain time intervals.
These and many other methods typically seek to maximize system throughput by reducing the interaction of calls or messages that are already inside the system, thereby allowing processor capacity to be dedicated to perform "useful" work. Useful work contributing to system "goodput" is measured as the rate of calls or messages that complete their functions within a specified time interval and/or with other desirable performance characteristics. Some prior art solutions have proven valuable under particular circumstances and for particular types of calls or messages, but none have been found to be applicable to the full range of overload conditions encountered in processor-based telecommunications systems handling different call classes.